IOS 8 - Screen freezes accessing Recent call log items

Question

We are having many problems with the devices upgraded to iOS8 (8.01, 8.0.2 and 8.1). The problem is the loss of Dialpad phone.
The iPhone 5 and 5c are extremely slow to navigate in the options inside the icon "Phone". For example, the keyboard appears when I enter the phone and can dial normally, however when I click to see the recent calls log, it crashes, it takes around 30-40 seconds to open the list of recent, after that we can return to keyboard and connect. If at that time, we click on Recent constantly, the screen goes white and locks the keyboard, you can no longer make calls or resetting the device only coming from the factory settings.
The problems intensify after enrolling into de ActiveSync environment, but we have tested several e-mail accounts and the same problems happen for all devices in Brazil, we also made these tests on devices from US personnel and the error does not occur.
iPhone 5 - Model A1428
Carrier: Claro Brasil 18.0
Model: MD643BZ/A

Answer 1

I have had the same problem but here is some additional information.
I am based in the UK but traveled to Brazil taking two iPhones (5c and 5s), both with IOS8.1.2, both with a UK contract with Vodafone.
Within 1 day of arriving both phones suffered the same problem: the "phone app" became unresponsive, with the favourites, recent, contacts and keypad buttons taking about 1 minute to have any effect. Sometimes the phone vibrated when a call was received but the phone app did not start so I could not answer the calls. The in-coming phone number was all zeros. The phone became useless.
Resetting the phones did not work.
When I got back to the UK the phones were both still unresponsive - it was as if the phone app had been "infected" in Brazil and would now not work.
I backed-up one of the phone, restored the iPhone loading 8.1.3, restored from the backup and the problem remained.
The only fix that I have found is to completely rebuild the iPhone, not restoring from the backup.
What I don't understand is how connecting to a Brazillian phone network caused these issues and why the stayed when I was no longer connected to it!